Preparation of hydrophobic organic aeorgels

ABSTRACT

Synthetic methods for the preparation of hydrophobic organics aerogels. One method involves the sol-gel polymerization of 1,3-dimethoxybenzene or 1,3,5-trimethoxybenzene with formaldehyde in non-aqueous solvents. Using a procedure analogous to the preparation of resorcinol-formaldehyde (RF) aerogels, this approach generates wet gels that can be dried using either supercritical solvent extraction to generate the new organic aerogels or air dried to produce an xerogel. Other methods involve the sol-gel polymerization of 1,3,5 trihydroxy benzene (phloroglucinol) or 1,3 dihydroxy benzene (resorcinol) and various aldehydes in non-aqueous solvents. These methods use a procedure analogous to the one-step base and two-step base/acid catalyzed polycondensation of phloroglucinol and formaldehyde, but the base catalyst used is triethylamine. These methods can be applied to a variety of other sol-gel precursors and solvent systems. These hydrophobic organics aerogels have numerous application potentials in the field of material absorbers and water-proof insulation.

RELATED APPLICATION

This application relates to U.S. Provisional Application No. 60/292,238filed May 18, 2001 and claims priority thereof.

PREPARATION OF HYDROPHOBIC ORGANIC AEORGELS

The United States Government has rights in this invention pursuant toContract No. W-7405-ENG-48 between the United States Department ofEnergy and the University of California for the operation of LawrenceLivermore National Laboratory.

BACKGROUND OF THE INVENTION

The present invention relates to solvent removal from water withhydrophobic aerogels, particularly to the preparation of hydrophobicorganic aerogels, and more particular to synthetic methods for thepreparation of hydrophobic organic aerogels.

The key property of the porous materials that inhibits wetting by liquidwater, is hydrophobicity. This property requires that the interfacialenergy of the solid-liquid, is greater than that for the solid-vapor.Such a property is inherent for many polymers; the best examples ofwhich are polyethylene, and polytetrafluoroethylene (Teflon). Othermaterial such as carbons and inorganic oxides, including aerogels,generally have low liquid-solid interfacial energies and their surfaceshave to be chemically modified to make them hydrophobic.

Aerogels are a special class of open-cell foams derived from highlycrosslinked inorganic or organic gels that are dried using specialtechniques to preserve the tenuous solid network. These materials haveultrafine cell/pore sizes, continuous porosity, high surface area, and amicrostructure composed of interconnected colloidal-like particles orpolymeric chains with characteristic diameters of 100 Å. Thismicrostructure is responsible for the unusual optical, acoustical,thermal, and mechanical properties of aerogels. By definition, thesematerials are prepared through the sol-gel process and can be eithergranular or monolithic. Organic aerogels are typically prepared from thesol-gel polymerization of resorcinol and formaldehyde and are driedthrough supercritical extraction of the reaction solvent. Recent effortshave focused on the ability to tailor the bulk properties of organicaerogels for specific applications. One area of interest is the designof hydrophobic organic aerogels.

While there are several reported ways to make hydrophobic silicaaerogels, it has been found that silica aerogels which are doped withfluorinated organic groups exhibit the highest degree of hydrophobicity.By measurement of the contact angles for a variety of hydrophobicaerogels, including tri-methyl, tri-fluoro, and methoxy terminatedsiloxanes, it has been determined that the 3,3,3-trifluoropropylcontaining aerogels have the highest contact angles for all cases ofsilica aerogels. It was found that silica aerogels doped with 30% byweight of the flouro-propyl compound, gave a contact angle ≧150°, andwas transparent. Such hydrophobic inorganic or silica aerogels aredescribed and claimed in copending U.S. applications Ser. No.09/957,854, filed Sep. 21, 2001, entitled “Method For Removing OrganicLiquids From Aqueous Solutions and Mixtures”; Ser. No. 09/957,853, filedSep. 21, 2001, entitled “Super-Hydrophobic Fluorine Containing Aerogels;and Ser. No. 09/960,593, filed Sep. 21, 2001, entitled “Method of OilSpill Recovery Using Hydrophobic Sol-Gels and Aerogels”. Also, see L. W.Hrubesh, “Solvent Removal from Water with Hydrophobic Aerogels, J.Nanocrystalline Solids” 285 (1-3), 328-32, 2001, for the verification ofhydrophobic silica aerogels.

The present invention involves the use of the hydrophobic organicaerogels for removal or organics from an oil-water mixture for example,and more specifically the present invention provides synthetic methodsfor the preparation of hydrophobic organic aerogels. One of thesemethods particularly involves the sol-gel polymerization of1,3-dimethoxybenze or 1,3,5-trimethoxybenzene with formaldehyde innon-aqueous solvents. Other of these methods involves the sol-gelpolymerization of 1,3,5-trihydroxy benzene or 1,3-dihydroxy benzene andvarious aldehydes in non-aqueous solvents. These methods can be appliedto a variety of other sol-gel precursors and solvent systems forproducing hydrophobic organic aerogels.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide hydrophobic organicaerogels.

A further object of the invention is to provide a method for preparationof hydrophobic organic aerogels.

Another object of the invention is to provide methods for preparation ofhydrophobic organic aerogels which can be utilized for a variety ofsol-gel precursors and solvent systems.

Another object of the invention is to provide methods for thepreparation of hydrophobic organic aerogels that involves the sol-gelpolymerization of 1,3-dimethorybenzene or 1,3,5-trimethoxybenzene withformaldehyde in non-aqueous solvents.

Another object of the invention is to provide methods for thepreparation of hydropholic organic aerogels that involves the sol-gelpolymerization of 1,3,5-trihydroxy benzene (phloroglucinol) or1,3-dihydroxy benzene (resorcinol) and various aldehydes in non-aqueoussolvents.

Other objects and advantages of the invention will become apparent fromthe following description. Basically, the invention involves hydrophobicorganic aerogels and methods for the preparation thereof. These aerogelshave potential utility as new sorbants for the removal of organicpollutants from water supplies or as water-proof insulation. While onethe methods is described, for example, involving sol-gel polymerizationof 1,3,5-trimethoxybenzene and formaldehyde in N,N-dimethylformamide,the method can be applied to a variety of other alkylated phenolderivatives and solvent systems, such as 1,3,5-trihydroxy benzene(phloroglucinol) or 1,3-dihydroxy benzene (resorcinol) and variousaldehydes (ethanol, propanal, benzyaldehyde, glutaricdialdehyde, and4,4,4-trifluorobutanal) in non-aqueous solvents. Using a procedureanalogous to the preparation of resorcinol-formaldehyde (RF) aerogels,or a procedure analogous to both the one-step base andtwo-stepbase/acid-catalyzed polycondensation of phloroglucinal andformaldehyde. These methods generate wet flexible gels that can be driedusing either supercritical solvent extraction to generate the new(hydrophobic) organic aerogels or dried to produce the xerogel. Themethod of this invention involves a simple and straightforward processfor the generations of hydrophobic organic aerogels.

DETAILED DESCRIPTION OF THE INVENTION

The present invention involves a hydrophobic organic aerogels and thepreparation thereof. More specifically the invention involves syntheticmethods for the preparation of hydrophobic organic aerogels utilizing asol-gel polymerization technique of selected materials. For example, ahydrophobic organic aerogel can be produced by a process involving thesol-gel polymerization of 1,3-dimethoxybenzene or1,3,5-trimethoxybenzene with formaldehyde in non-aqueous solvents. Usinga procedure analogous to the preparation of resorcinol-formaldehyde (RF)aerogels, such as disclosed in U.S. Pat. Nos. 5,476,878 and 5,731,360,for example, this approach generates wet gels that can be dried usingeither supercritical solvent extraction to generate the hydrophobicaerogels or air dried to produce the hydrophobic xerogels. Also, ahydrophobic organic aerogel can be produced by a process involving thesol-gel polymerization of 1,3,5-trihydroxy benzene (phloroglucinol) or1,3-dihydroxy benzene (resorcinol) and various aldehydes (ethanol,propanal, benzyaldehyde, glutaricdialdehyde, and 4,4,4-trifluorobutanalin non-aqueous solvents, using a procedure analogous to both theone-step base and two-step base/acid-catalyzed polycondensation ofphloroglucinol and formaldehyde, but where the base catalyst used intriethylamine, and the acid catalyst used in hydrochloric acid. Theselater methods generate wet rigid gels that can be dried using eithersupercritical solvent extraction to make aerogels or air dried toproduce xerogels. On one such material, an aerogel from thepolycondensation of phloroglucinol and propyl aldehyde, water forms atight bead with a contact angle of ˜145°. The procedures of thisinvention as exemplified hereinbelow are general and can be applied to avariety of other sol-gel precursors and solvent systems. Thesehydrophobic aerogels possess unique and interesting properties and finduse in the field of filtration, such as for removing organic pollutantsfrom water, field of insidation, including water-proof insulation.

The present invention is first exemplified by the sol-gel polymerizationof 1,3-dimethoxybenzene and formaldehyde in N,N-dimethylformamide. Thisprocedure, however, is general and can be applied to a variety of otheralkylated phenol derivatives, such as 1,3,5-trimethoxybenzene andformaldehyde, methoxybenzene and formaldehyde, and solvent systems suchas DMSO, THF, acetone, and acetonitrile.

An example of this procedure is as follows:

To a solution of 1,3,5-trimethoxybenzene (18.8 g, 0.112 mol) inN,N-dimethylformamide (140 mL) was added a mixture of Na₂CO₃H₂O (0.139g, 0.0011 mol) in 37% formaldehyde solution (22.4 g, 0.224 mol) inwater. The reaction mixture was stirred vigorously at room temperaturefor 0.5 hour. The clear solution was then poured into glass vials,sealed and cured at 80° C. for 3 days during which time the reactionturned to a dark orange color. While this procedure did not yieldmonolithic parts, it did afford a light yellow organic gel as aprecipitate. The gel was then dried by both known procedures. Thesol-gel was characterized for information such as density, surface area,pore volumes of the materials.

The present invention is next exemplified by the sol-gel polymerizationof 1,3,5-trihydroxybenzene (phloroglucinol) and propanal inacetonitrile. This procedure is general and can be applied to thepreparation of a variety of other aldehyde crossliker systems, similarto, but not limited to ethanol, benzyaldehyde, glutaricdialdehyde, and4,4,4-trifluorobutanal. Also, the method can be carried out by thesol-gel polymerization f 1,3-dihydroxy benzene (resorcinol) and theabove listed aldehydes. This exemplified procedure is as follows:

0.5 g of 1,3,5-trihydroxybenzene trihydrate (0.003 mol) was dissolved in9 grams of acetonitrile (11.5 mL). To this solution 0.5 g of acetonitilewith 0.017 mL of triethyleamine (0.00012 mol) in it was added to thestirring solution. The addition of triethylamine causes the instantformation of a white precipitate that dissolves rapidly in the stirringsolution to give a clear faint yellow solution. To this solution 0.36 gof propanal (0.006 mol) is added. The vessel the solution is in is thencovered tightly and put into an oven at 80° C. for one hour. During thistime, the solution changes color from light yellow to a dark red/orangecolor, however, the solution remains clear. After cooling to roomtemperature, 0.5 g of acetonitrile with 0.030 mL (0.0036 mol) ofconcentrated commercial hydrochloric acid was added to the clearred/orange solution. Within seconds of the addition of the acidcatalyst, the solution becomes warm to the touch and within 1-2 minutes,a rigid clear red/orange gel was formed. This gel was extracted withliquid CO₂ and then supercritically extracted to give a robust aerogelwith a density of 145 mg/cc, surface area of 413 m²/g, average porediameter of 28.4 nm, and a pore volume of 3.49 cm³/g. This synthesis canalso be performed using just the one-step base catalyst (triethylamine);however, gel times in these cases are on the order of a few days. Inaddition, as pointed out above, the above procedure is possible using1,3-dihydroxybenzene (resorcinol) as the phenolic starting material.

It has thus been shown that the present invention provides hydrophobicorganic aerogels, and methods for producing such from a variety ofalkylated phenol derivatives and solvent systems.

While particular procedures, materials, processing parameters has beendescribed to exemplify and each the principles of the invention, suchare not intended to be limited. Modifications and changes may becomeapparent to those skilled in the art, and it is intended that theinvention be limited only by the scope of the appended claims.

What is claimed is:
 1. A method for producing an organic hydrophobicmaterial, comprising: providing an alkylated phenol derivative,providing an aldehyde, providing a catalyst, providing a non-aqueoussolvent system, and carrying out sol-gel polymerization of a mixture ofthe alkylated phenol derivative and the aldehyde in the non-aqueoussolvent system.
 2. The method of claim 1, additionally including adrying operation to produce one of a hydrophobic organic aerogel or ahydrophobic organic xerogel.
 3. The method of claim 2, wherein thedrying operation to produce the aerogel is supercritical solventextraction.
 4. The method of claim 2, wherein the drying operation toproduce the xerogel is air drying.
 5. The method of claim 1, wherein thealkylated phenol derivative is selected from the group consisting of1,3-diemthoxybenzene, 1,3-5-trimethoxybenzene and methoxybenzene and thealdehyde is formaldehyde.
 6. The method of claim 1, wherein thenon-aqueous solvent system is N,N-dimethylformamide.
 7. A methodcomprising: providing a 1,3,5-trimethyoxybenzene solution of1,3,5-trimethyoxybenzene in N,N-dimethylformamide, adding the1,3,5-trimethyoxybenzene solution to a 35% formaldelyde solutioncontaining a quantity of Na₂CO₃H₂O to form a combined solution, stirringthe combined solution at room temperature for a time period, pouring thecombined solution into at least one container, sealing the container,and curing the contained combined solution at a temperature above roomtemperature for a period of time.
 8. The method of claim 7, wherein the1,3,5-trimethoxybenzene comprises at least about 15.0 g, 0.112 mol. 9.The method of claim 7, wherein the N,N-dimethylformamide comprises atleast about 125 mL.
 10. The method of claim 7, wherein the NagCO₃H₂Ocomprises at least about 0.125 g, 0.0011 mol.
 11. The method of claim 7,wherein the stirring time period is at least about 0.4 hr.
 12. Themethod of claim 7, wherein the curing is carried out at above 75° C. fora time period of at least 2 days.
 13. A method comprising: stirringsolution of 1,3,5-trihydroxybenzene trihydrate in acetonitrile, addingto the stirring solution a quantity of acetonitile with triethyleamine,adding to the thus formed solution a quantity of propanal, containingthe thus formed solution in a vessel, covering the vessel containing thesolution, placing the vessel in an oven at a selected temperature for aspecified time period, cooling the solution to room temperature, andadding to the cooled solution a quantity of acetonitrile withconcentrated hydrochloric acid, to form a gel.
 14. The method of claim13, additionally comprising: extracting the gel with liquid CO₂, andthen supercritically extracting the CO₂ to produce an aerogel.
 15. Themethod of claim 13, wherein the 1,3,5-trihydroxybenzene trihydratecomprises at least about 0.4 g (0.0025 mol), and the acetonitrilecomprises at least about 8 g (10 mL).
 16. The method of claim 13,wherein the added acetonitile with triethyleamine comprises at leastabout 0.4 g of acetonitile with at least about 0.15 mL.
 17. The methodof claim 13, wherein the quantity of propanal comprises at least about0.3 g (0.005 mol).
 18. The method of claim 13, wherein the temperatureis at least 75° C. and the time period is at least ¾ hour.
 19. Themethod of claim 13, wherein the quantity of acetonitrile withconcentrated hydrochloric acid comprises at least 0.4 g of acetonitrilewith at least about 0.025 mL (0.0030 mol) of concentrated hydrochloricacid.